The long term objective of the proposed research is to determine how microtubule assembly and function are modulated by microtubule-associated proteins (MAP). It is proposed to continue our studies on the distribution and expression of a particular MAP, MAP 4, using a number of approaches. The location of MAP 4, or MAP 4 subspecies, in early mouse embryos, or at various stages of fetal development, will be analyzed using immunocytological techniques. The results from these studies will be correlated with in situ hybridization analyses of the expression of the MAP 4 genes. A second set of studies will employ microinjection and fluorescence redistribution after photo-bleaching (FRAP) technologies to investigate how MAP-microtubule interactions are modulated in cells. It is proposed to continue studies on the dynamics on MAP, using modified proteins epitope specific antibodies, to try to ascertain which regions of the MAP molecule may be important in the functioning of microtubules in vivo. A third project involves identifying the sequences coding for MAP 4, and the use of these clones to quantify the expression of MAP 4, or MAP 4 subspecies during various developmental stages. These studies should provide basic information on the biological role of microtubule-associated proteins in the organization of microtubules in developing organisms and in individual cells.